5th International Conference on Spoken Language Processing
Infant Directed Speech (IDS) samples were collected longitudinally from six mothers speaking to their infants (three with female infants and three with male infants) when their infants were newborns, 3 months, 6 months, 9 months and 12 months of age. Adult Directed Speech (ADS) samples of these mothers were also collected to be compared with these IDS samples. This maternal speech was then examined in terms of the phonetic characteristics, specially the prosodic aspects-pitch, tempo, and loudness. Twenty utterances from each of the six mothers speaking to their infants at each of the five ages and to an adult, totaling 720 utterances (20 utterances x 6 mothers x 6 age groups) were acoustically analyzed. They are fundamental frequencies, frequency ranges, utterance duration, syllable duration, numbers of syllable per utterance, and intensity values. Results of the comparison between IDS and ADS showed that IDS used higher fundamental frequencies (263.3 Hz vs 247.99 Hz), greater frequency range in semitones (15.16 st vs 13.5 st), shorter utterance duration (1106 ms vs 1506 ms), longer syllable duration (343 ms vs 220 ms), and less numbers of syllable per utterance (3.85 vs 7.63). Concerning the age-related changes of prosodic features, there seems to be three age intervals which show unique modification to the pattern of prosodic characteristics. The first age group is the newborns as opposed to other age groups, mothers use longer utterance duration, longer syllable duration, and more numbers of syllable per utterance. In the 3- and the 6-month-old periods, the mothers' speech style changes to an increase of the mean Ff and pitch modulation. By the time the infants reach 9 and 12 months of age, there is a successive decrease of Ff of the speech directed to the 6MO to the 9MO and the 12MO. Most prosodic features of the IDS directed to the 12MO are almost similar to those of the ADS. The study of intensity values in IDS fails to reveal any significant variation due to a general phonetic problem in the instrumental study of the degree of loudness in speech. The variations of the phonetic characteristics among the 6 groups in all aspects were statistically analyzed using the Analysis of Variance (ANOVA). It was found that every variation of the prosodic features investigated across age groups was statistically significant. It seems that these phonetic characteristics in the mothers' speech are adjusted to accommodate the communicative functions between the mothers and their infants and these functions have developed according to other developments of the infants.
Bibliographic reference. Thanavisuth, Chayada / Luksaneeyanawin, Sudaporn (1998): "Acoustic qualities of IDS and ADS in Thai", In ICSLP-1998, paper 0912.